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x86/apic: Fix x2apic enablement without interrupt remapping

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[ Upstream commit 26573a97746c7a99f394f9d398ce91a8853b3b89 ]

Currently, Linux as a hypervisor guest will enable x2apic only if there are
no CPUs present at boot time with an APIC ID above 255.

Hotplugging a CPU later with a higher APIC ID would result in a CPU which
cannot be targeted by external interrupts.

Add a filter in x2apic_apic_id_valid() which can be used to prevent such
CPUs from coming online, and allow x2apic to be enabled even if they are
present at boot time.

Fixes: ce69a78450 ("x86/apic: Enable x2APIC without interrupt remapping under KVM")
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201024213535.443185-2-dwmw2@infradead.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
David Woodhouse
2020-10-24 22:35:01 +01:00
committed by Greg Kroah-Hartman
parent 459c15dd68
commit b8ab21e017
3 changed files with 18 additions and 6 deletions
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9
arch/x86/kernel/apic/x2apic_phys.c
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@@ -8,6 +8,12 @@
int x2apic_phys;
static struct apic apic_x2apic_phys;
static u32 x2apic_max_apicid __ro_after_init;
void __init x2apic_set_max_apicid(u32 apicid)
{
x2apic_max_apicid = apicid;
}
static int __init set_x2apic_phys_mode(char *arg)
{
@@ -98,6 +104,9 @@ static int x2apic_phys_probe(void)
/* Common x2apic functions, also used by x2apic_cluster */
int x2apic_apic_id_valid(u32 apicid)
{
if (x2apic_max_apicid && apicid > x2apic_max_apicid)
return 0;
return 1;
}